The Inner Ear - A Closed Shop With a Division of Labor
The inner ear contains the sensory systems of balance and hearing. Its location is close to the center of the skull and it is encased in the hardest bones in the body which make it one of the best protected sensory systems. This protection reflects the importance of the hearing and balance for survival. The organs of balance are much older than those of hearing and evolved with the earliest multicellular organisms. All vertebrate balance organs are similar in structure and function. The organ of hearing evolved from one of the balance organs and this heritage is retained when it buds off from the balance organ early in fetal development. The basic structure of the human inner ear is present in the fetus at 6 months and hearing begins before birth. The auditory portion of the inner ear of mammals differs structurally from that of birds, reptiles and fish but its function in all animals is the same - to tell the brain how much energy is contained in an environmental sound and at what frequencies that energy is located.
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